Field of the Invention
The present invention concerns a pallet lever for the escapement mechanism of a watch movement, particularly a Swiss lever escapement.
Description of Related Art
A pallet lever for a timepiece escapement mechanism is disclosed in EP Patent Application No 2320280. In order to optimise the respective functions of the fork and the lever, the fork is an added part, offset from the plane of the lever and the guard pin. The fork is secured to the lever by means of a stud driven into the respective orifices made in the fork and the lever, the stud also creating the distance between the plane of the lever and of the fork. This distance along an axis perpendicular to the general plane of the pallet lever must be perfectly controlled during manufacture of the pallet lever and particularly during assembly of the guard pin on the lever in order to obtain optimal operation of the mechanism in which the pallet lever is integrated. By way of illustration, the manufacturing tolerance for creating this distance is typically on the order of ±20 μm. In conventional practice, the studs are metal parts of very small diameters made by bar turning. Typically, these studs are produced by bar turning a steel, brass or nickel silver bar. These studs typically have a diameter of around 0.24 mm.
A current problem with bar turned studs is that they have “teats” on the front faces thereof resulting from the parting-off operation during manufacture. Indeed, when the chisel separates the stud from the bar of material at the end of the bar turning operation, the stud is released from the bar and a small cone of material remains on the end surfaces. This small cone of material known as a “teat” is not desired, since it makes it impossible to form a clean end face perpendicular to the cylinder able to serve as reference for an operation to assemble the guard pin on the lever with a precise distance. These studs cannot be driven in “flush” with the lever. Further, it is difficult to assemble the studs since, due to their small dimensions, they tend to deform during assembly resulting in a permanent loss in positioning of the fork relative to the guard pin, which has a negative effect on the performance of the escapement device.